The present invention generally relates to methods for backup of data stored in a computer system, and particularly to a method for backup of data by using the data copying function of a disk array system and its function to acquire frozen images of data (snapshot function), and to a system using this method.
The computer system is now required to always make stable operation and to avoid the situations in which the computer system halts the service because of accident or maintenance. In addition, even if a trouble occurs on the computer system by any possibility, it is necessary to minimize the loss of data within the computer system, and to restore the system to its former state as soon as possible.
In the prior art, data-updating operation is regularly frozen (freezing), and at this time data is copied (backed up) onto a storage medium such as inexpensive magnetic tape. Thus, if some data is lost by a fault, the data is recovered (restored) from the tape, thus full data being kept safe. On the tape are stored not only the data and control information necessary for the computer system, but also information necessary for the management for the data to be backed up by using part of the storage region of the tape.
This management information includes codes for identifying the data contents and the dates on which the backup data was acquired as, for example, described in “File Structure and Labeling of Magnetic Tapes for Information Exchange”, 4th Edition, Standard ECMA-13, December, 1985, pp. 7–19. The software (backup software) for controlling the backup and restore processes usually manages the list (catalog) of the produced backup data, and when the externally produced backup data is added and managed, it adds necessary information to the catalog by referring to the management information recorded on the tape.
Recently, use of “on-line backup” has advanced. This on-line backup uses “data mirror function” or “snapshot function” to generates a backup image (snapshot) quickly so that data can be copied onto the tape while a computer system is operating. The data mirror function duplicates data on a plurality of storage regions (disk volumes) and freeze one of the regions as a snapshot of data according to need. The snapshot function saves, at the time of data update, the data to be updated before update and provide a frozen image of the disk volume at a certain time point with both the current disk volume content and the before-update data. These functions are provided in the software on the computers or disk arrays.
The data mirror function is disclosed in, for example, U.S. Pat. No. 5,845,295, and the snapshot function in, for example, U.S. Pat. No. 5,649,152.